Conductive resin film, collector and production methods therefore

ABSTRACT

There is disclosed a conductive resin film comprising a conductive substrate layer and a low-resistance layer with a volume resistance of 0.1 to 1.0 Ωcm including a fine carbon fiber and a resin in a thickness direction on at least one of its outermost layer. This film exhibits good conductivity even with a low mixing rate of the conductive material and good acid resistance.

TECHNICAL FIELD

This invention relates to a monolayer or laminated resin film withimproved conductivity; particularly, for example, a conductive resinlaminated film comprising a low-resistance layer containing a finecarbon fiber with significantly higher corrosion resistance. Thisinvention also relates to a process for manufacturing the conductiveresin film and further relates to a collector used in an electric doublelayer capacitor.

BACKGROUND ART

In the field of electronics, major properties required for a polymermaterial include moldability, heat resistance, durability, highconductivity, corrosion resistance, recyclability and electromagneticwave blocking effect, depending on a product and an application. Ingeneral, polymer materials used in this field include thermosettingresins such as epoxy resins and phenol resins; and engineering plasticssuch as polyphenylene oxides, liquid crystal polymers, polyimides andpolycarbonates.

However, although a material generally having the above properties isstrongly needed, producing such a material is generally difficult, oftenresulting in a disadvantageous cost. One of such required properties ishigher conductivity, and in addition to the property, there is needed apolymer material further exhibiting good corrosion resistance.

Japanese Patent Publication No. 1991-77288 has proposed a fine carbonfiber with higher conductivity as a conductive material. However, whenbeing combined with a resin, such a fine carbon fiber is lessdispersible, leading to insufficient conductivity. Specifically, asdescribed in Japanese Patent Laid-open Publication No. 1995-102112, aproduct obtained by blending a resin (80% by weight) with a fine carbonfiber (20% by weight) in a dry blending process and then molding themixture by an extruder has a volume resistivity as high as about 1 Ω,which is insufficient conductivity. Japanese Patent Laid-openPublication No. 1991-55709 has described a conductive sheet wherein aparticular hollow carbon fibril is dispersed in an insulative polymermaterial, but it has an inadequate volume resistivity.

One of applications requiring conductivity and corrosion resistance isan electric double layer capacitor using an aqueous electrolyticsolution. An electric double layer capacitor is an electric elementconsisting of a pair of polarizable electrodes, collectors and anelectrolyte. Such capacitors can be generally classified into thosecomprising an organic solvent type electrolytic solution or an aqueouselectrolytic solution.

Comparing these two types of capacitors, a capacitor comprising anaqueous electrolytic solution can generally give a lower output voltagethan a capacitor comprising an organic solvent electrolytic solution,but it has larger ion conductivity in the electrolytic solution, so thatan internal resistance of the capacitor may be reduced to give anadvantageously larger output current. Furthermore, a capacitorcomprising an aqueous electrolytic solution is advantageous in thathandling thereof is easy from a view point of safety, because it doesnot comprise a flammable liquid as used in a capacitor comprising anorganic solvent electrolytic solution,

An electric double layer capacitor comprising an aqueous electrolyticsolution has a configuration as shown in FIG. 1, where polarizableelectrodes 2 are placed opposite each other via a separator 4,collectors 1 are placed outside of the individual polarizable electrodes2 and are insulated by a gasket 3.

When using a plurality of capacitors are connected in series or inparallel for obtaining a higher output voltage in an electric doublelayer capacitor comprising an aqueous electrolytic solution, an internalresistance of the capacitor-composite as a whole may be increased,resulting in a lower output current. Thus, it has been desired to reducean internal resistance of each capacitor as much as possible.

It is well-known that an internal resistance in each capacitor isgenerated from an aqueous electrolytic solution, polarizable electrodes,collectors and interfaces therebetween. Reduction of internal resistancein a capacitor has been conducted by, for example, reducing a volumeresistance in the collector.

Commonly used collectors include conductive rubber films (for example,see Japanese Patent Laid-open Publication Nos. 2000-12388 and1993-94925). These comprise a rubber containing conductive carbon andthe like and have generally a volume resistance of about 10 to 100 Ωcm.Thus, there have been needs for a material having a further lower volumeresistance.

Additionally, an electric double layer capacitor comprising an aqueouselectrolytic solution comprises an about 25 to 50% aqueous sulfuric acidsolution as an electrolytic solution. A collector must be, therefore,also acid resistant.

A known example of the above collector is a conductive resin film inwhich a conductive material is a metal (see Japanese Patent Laid-openPublication No. 2000-12388), but it has a drawback that its conductivityis unstable under an acidic environment. When using a noble metal withgood corrosion resistance as a conductive material, a cost becomesextremely higher, while a carbon-containing conductive material haslower conductivity than a metal, resulting in inadequate conductivity.

List of References

For a conductive resin film, Japanese Patent Publication No. 1991-77288and Japanese Patent Laid-open Publication Nos. 1995-102112 and1991-55709;

For an electric double layer capacitor, Japanese Patent Laid-openPublication Nos. 2000-12388 and 1993-94925.

DISCLOSURE OF THE INVENTION

An objective of an aspect of this invention is to provide a conductiveresin film having good conductivity and acid resistance, and a processfor manufacturing thereof.

An objective of another aspect of this invention is to provide acollector for an electric double layer capacitor, which has goodconductivity and acid resistance.

A first aspect of this invention provides a conductive resin filmcomprising a low-resistance layer, a manufacturing process therefor anda collector produced thereby, and relates to the following items (1) to(8).

(1) A conductive resin film comprising a conductive substrate layer anda low-resistance layer with a volume resistance of 0.1 to 1.0 Ωcm in athickness direction as at least one of its outermost layer.

(2) The conductive resin film as described in the above (1), wherein avolume resistance of the low-resistance layer in a thickness directionis ⅕ or less of a volume resistance of the substrate layer in athickness direction.

(3) The conductive resin film as described in the above (1) or (2),wherein the low-resistance layer is a layer in which the thermoplasticresin comprises a fine carbon fiber with a fiber diameter of 0.003 to0.5 μm and a fiber length of 0.1 to 100 μm as a conductive agent.

(4) The conductive resin film as described in any of the above (1) to(3), wherein a thickness of the low-resistance layer is 1 to 50 μm.

(5) The conductive resin film as described in any of the above (1) to(4), wherein the substrate layer comprise a conductive agent selectedfrom the group consisting of graphite powder, exfoliated graphite,carbon black, carbon fiber, carbon nanofiber, carbon nanotube, a metalcarbide, a metal nitride, a metal oxide, metal fiber and metal powder.

(6) A process for manufacturing a conductive resin film having alow-resistance layer as at least one of its outermost layers, comprisingthe steps of applying a liquid composition of a fine carbon fiber and athermoplastic resin in a solvent to a flat surface of a support,followed by drying or curing to form a coating film; placing the coatingfilm over at least one side of a conductive substrate layer; andperforming a lamination.

(7) A conductive resin film as described in any of the above (1) to (5)used as a collector for an electric double layer capacitor.

(8) A collector for an electric double layer capacitor comprising theconductive resin film as described in the above (7).

A second aspect of this invention provides a low-resistance monolayerconductive resin film, a manufacturing process therefor and a collectortherewith, and relates to the following items (9) to (14).

(9) A conductive resin film comprising a thermoplastic resin containinga fine carbon fiber having a fiber diameter of 0.001 to 0.5 μm and afiber length of 0.1 to 100 μm, wherein when a mixing volume ratio of thethermoplastic resin to the fine carbon fiber is expressed by theequation:Thermoplastic resin/Fine carbon fiber=x/(100−x)and a volume resistance of the film is y in Ωcm, a coordinate point(x,y) in a x-y plane is within a range enclosed by a quadrangle withfour apices (50,0.01), (50,0.03), (90,0.1) and (90,0.5) including thelines and the apices.

(10) The conductive resin film as described in the above (9), wherein athickness of the conductive resin film is 10 to 200 μm.

(11) A process for manufacturing a conductive resin film, comprising thesteps of applying a liquid composition of a fine carbon fiber having afiber diameter of 0.001 to 0.5 μm and a fiber length of 0.1 to 100 μmand a thermoplastic resin in a solvent to a flat surface of a support,followed by drying or curing to form a coating film; and then peelingthe coating film from the support.

(12) A conductive resin film manufactured by the process as described inthe above (11).

(13) The conductive resin film as described in any of the above (9),

(10) and (12) used as a collector for an electric double layercapacitor.

(14) A collector for an electric double layer capacitor comprising theconductive resin film as described in the above (13).

A third aspect of this invention provides a collector with a lowresistance and a higher tensile breaking strength, and relates to thefollowing items (15) to (23).

(15) A collector for an electric double layer capacitor consisting of aconductive resin film comprising a thermoplastic resin containing aconductive agent, wherein the film has a volume resistance in athickness direction of 0.01 to 5 Ωcm and a tensile breaking strength of10 to 30 MPa as measured in accordance with JIS K7127.

(16) The collector for an electric double layer capacitor as describedin the above (15), wherein the thermoplastic resin is selected from thegroup consisting of fluororesins, fluoro-rubbers, polyolefins andpolyolefin elastomers.

(17) The collector for an electric double layer capacitor as describedin the above (15) or (16), wherein the conductive agent is selected fromthe group consisting of carbon nanotube, carbon nanofiber, a metalcarbide and a metal nitride.

(18) The collector for an electric double layer capacitor as describedin any of the above (15) to (17), wherein a volume ratio of thethermoplastic resin to the conductive agent is 50/50 to 90/10.

(19) The collector for an electric double layer capacitor as describedin any of the above (15) to (18), wherein a thickness of the conductiveresin film is 0.01 mm to 0.5 mm.

(20) The collector for an electric double layer capacitor as describedin any of the above (15) to (19), wherein at least one side of theconductive resin film comprises a low-resistance layer.

(21) A process for manufacturing a collector for an electric doublelayer capacitor, comprising the steps of forming a conductive layer on apeelable support, placing the conductive layer with the support over atleast one side of the conductive substrate layer to transfer theconductive layer, and peeling the support to form a low-resistance layeron the surface of the conductive resin film.

(22) A collector for an electric double layer capacitor manufactured bythe process as described in the above (21).

(23) The collector for an electric double layer capacitor as describedin any of the above (15) to (20) and (22), wherein the electric doublelayer capacitor comprises an aqueous electrolytic solution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of an aqueous electric double layercapacitor.

FIG. 2 schematically shows an apparatus for measuring a volumeresistance in a thickness direction.

FIGS. 3A and 3B are SEM images of a cross-section and a surface of aconductive resin film whose surface is comprised of a low-resistancelayer comprising a fine carbon fiber as a conductive agent,respectively.

In the drawings, the symbols have the following meanings; 1: collector,2: polarizable electrode, 3; gasket, 4: separator, 11: brass electrode(having a gold-plated surface), 12: sample.

BEST MODE FOR CARRYING THE INVENTION

This invention will be described in detail.

In this invention, a volume resistance in a thickness direction is avalue obtained by converting a resistance in a film thickness directionincluding a contact resistance of a surface into a volume resistance.Specific method of measurement will be described in Examples. -ps<<Description of Materials>>

<Resin as a Film Component>

A resin used for a film of this invention is preferably a thermoplasticresin. Examples of a thermoplastic resin include, but not limited to,polyolefin (PO) resins and polyolefin elastomers such asethylene-containing homopolymers and copolymers; amorphous polyolefinresins (APO) such as cyclic polyolefins; polystyrene resins such aspolystyrene (PS), ABS and SBS, and hydrogenated styrene elastomers suchas SEBS; polyvinyl chloride (PVC) resins; polyvinylidene chloride (PVDC)resins; (meth)acrylate and (meth)acrylic resins such as polymethylmethacrylate (PMMA) and copolymerized acryls; polyester resins such aspolyethylene terephthalate (PET); polyamide (PA) resins such as Nylon 6,Nylon 12 and copolymerized Nylons; polyvinyl alcohol resins such aspolyvinyl alcohol (PVA) resins and ethylene-vinyl alcohol copolymers(EVOH); polyimide (PI) resins; polyetherimide (PEI) resins; polysulphone(PS) resins; polyethersulphone (PES) resin; polyamide imide (PAI)resins; polyether-ether ketone (PEEK) resins; polycarbonate (PC) resins;polyvinyl butyral (PVB) resins; polyalylate (PAR) resins;polyphenylenesulfide (PPS) resins; and fluororesins andfluoro-elastomers.

Among these thermoplastic resins, resins with good heat resistance andacid resistance are preferably used, including polyolefin (PO) resinsand polyolefin elastomers, hydrogenated styrene elastomers such as SEBS,and fluororesins and fluoro-elastomers.

Examples of fluororesins and fluoro-elastomers may include at least oneor more of fluororesins or fluoro-rubbers selected from the groupconsisting of PTFE (polytetrafluoroethylene), PFA(tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), FEP(tetrafluoroethylene-hexafluoropropylene copolymer), EPE(tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ethercopolymer), ETFE (tetrafluoroethylene-ethylene copolymer), PCTFE(polychlorotrifluoroethylene), ECTFE (chlorotrifluoroethylene-ethylenecopolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride),THV (tetrafluoroethylene-hexafluoropropylene-vinylidene fluoridecopolymer), VDF-HFP (vinylidene fluoride-hexafluoropropylene copolymer),TFE-P (vinylidene fluoride-propylene copolymer), fluorine-containingsilicone rubbers, fluorine-containing vinyl ether rubbers,fluorine-containing phosphazene rubbers and fluorine-containingthermoplastic elastomers.

Among these, PVDF, THV, VDF-HFP and TFE-P which contain vinylidenefluoride are particularly preferable in the light of moldability.

Examples of polyolefin resins and polyolefin elastomers may include atleast one or more of polyolefins and polyolefin elastomers selected fromthe group consisting of polyethylene, polypropylene, polybutene,poly(4-methyl-1-pentene), polyhexene, polyoctene, hydrogenatedstyrene-butadiene rubbers, EPDM, EPM and EBM.

Among these, polyethylene, polypropylene, EPDM and hydrogenatedstyrene-butadiene rubbers are particularly preferable in the light ofheat resistance and moldability.

<Conductive Agent>

A conductive agent used in this invention makes a resin film conductive.

Examples of a carbon conductive agent include graphite powders such asnatural graphite, pyrolytic graphite and kish graphite; exfoliatedgraphite prepared by immersing the above-mentioned graphite in an acidicsolution and then expanding it by heating; Ketjen Black, acetylene blackand carbon black prepared by, for example, a furnace process; carbonfibers such as PAN-based type and pitch-based type; and carbonnanofiber, carbon nanotube and carbon nanohorn prepared by, for example,arc discharge, laser vaporization and vapor growth.

Examples of a metal carbide conductive agent include tungsten carbide,silicon carbide, zirconium carbide, tantalum carbide, titanium carbide,niobium carbide, molybdenum carbide, vanadium carbide, chromium carbideand hafnium carbide. Among others, tungsten carbide, titanium carbideand chromium carbide are particularly preferable for an applicationrequiring conductivity and acid resistance.

Examples of a metal oxide conductive agent include metal oxides such astitanium oxide, rhutenium oxide and indium oxide.

Examples of a metal nitride conductive agent include metal nitrides suchas chromium nitride, aluminum nitride, molybdenum nitride, zirconiumnitride, tantalum nitride, titanium nitride, gallium nitride, niobiumnitride, vanadium nitride and boron nitride. Among these, titaniumnitride and zirconium nitride are particularly preferable for anapplication requiring conductivity and acid resistance.

Examples of a metal conductive agent include metal fibers such as ironfiber, copper fiber and stainless fiber; and metal powders such astitanium powder, nickel powder, tin powder, tantalum powder and niobiumpowder.

<First Aspect of the Invention: a Conductive Resin Film in which anOutermost Layer Comprises a Low-Resistance Layer>

A conductive resin film according to the first aspect of the inventioncomprises a substrate layer and an outermost layer comprised of alow-resistance layer at least in one side. A volume resistance of thelow-resistance layer, which is lower than that of the substrate layer,contributes significantly to reduce a contact resistance of the filmwith a contacting article (i.e. article or parts to which the filmcontacts). It also contributes to reduce an overall mixing percentage ofthe conductive agent in the film as a whole.

Particularly, when using the conductive resin film of this invention asa collector for an electric double layer capacitor, a contacting articleis a carbon electrode or outer case (e.g., a stainless steel case). Insuch a case, a volume resistance of the low-resistance layer in theconductive resin film, which is lower than that of the substrate layer,contributes to reduce a contact resistance with a contacting article andthus to reduce an internal resistance of the electric double layercapacitor.

A volume resistance of the low-resistance layer in a thickness directionmust be within a range of 0.1 to 1.0 Ωcm. If it is more than 1.0 Ω cm,adequate conductivity cannot be obtained. A volume resistance of thelow-resistance layer in a thickness direction is ⅕ or less, preferably ⅛or less of a volume resistance of the substrate layer in a thicknessdirection. If a volume resistance of the low-resistance layer in athickness direction is more than ⅕ of a volume resistance of thesubstrate layer in a thickness direction, a contact resistance with acontacting article tends to be increased.

The low-resistance layer comprises a resin and a conductive agent. Theresin is preferably a thermoplastic resin, which can be, depending on anapplication, appropriately selected from the thermoplastic resins listedin “Resin as a film component”. Particularly preferred are polyolefin(PO) resins and polyolefin elastomers; hydrogenated styrene elastomerssuch as SEBS; and fluororesins and fluoro-elastomers with good heatresistance and acid resistance.

A conductive agent in the low-resistance layer is preferably a finefiber, particularly carbon fiber, which exhibits good corrosionresistance and conductivity. A fiber diameter of the fine carbon fiberis 0.003 to 0.5 μm, preferably 0.08 to 0.2 μm, and its fiber length is0.1 to 100 μm, preferably 1 to 50 μm for obtaining good conductivity.Examples of such a fine carbon fiber include carbon nanofiber and carbonnanotube and the like.

A mixing ratio of the resin (particularly, a thermoplastic resin) in thelow-resistance layer to the fine carbon fiber may be appropriatelyselected such that a volume resistance of the low-resistance layer in athickness direction come to be 0.1 to 1.0 Ωcm and ⅕ or less of a volumeresistance of the substrate layer in a thickness direction. Preferably,a volume ratio of the thermoplastic resin to the fine carbon fiber is15/85 to 85/15.

A thickness of the low-resistance layer is 1 to 50 μm, preferably 3 to20 μm. If a thickness of the low-resistance layer is less than 1 μm, thelayer is so thin that a pinhole tends to be formed in the low-resistancelayer, leading to the presence of a portion having a larger volumeresistance. If a thickness of the low-resistance layer is more than 50μm, the conductive resin film tends to be fragile. The low-resistancelayer may be formed on one or both of the sides of the substrate layer.

Next, there will be described a substrate layer in a conductive resinfilm.

A substrate layer is preferably a resin containing a conductive agent.The resin is preferably a thermoplastic resin, which can be, dependingon an application, appropriately selected from the thermoplastic resinslisted in “Resin as a film component”. Particularly preferred arepolyolefin (PO) resins and polyolefin elastomers; hydrogenated styreneelastomers such as SEBS; and fluororesins and fluoro-elastomers withgood heat resistance and acid resistance.

A conductive agent which can be contained in the substrate layer may beselected from those listed in “Conductive agent”. Particularly preferredan acid-resistant conductive agent such as a carbon conductive agent foran application requiring acid resistance.

A volume ratio of the thermoplastic resin to the conductive agent in thesubstrate layer is preferably, but not limited to, 30/70 to 90/10. If avolume ratio of the thermoplastic resin to the conductive agent is lessthan 30/70, a rate of the conductive agent is so high that fluidabilityof the resin may be inadequate to form thin film and the conductiveresin film may be fragile. If a volume ratio of the thermoplastic resinto the conductive agent is more than 90/10, a rate of the conductiveagent is too low to give adequate conductivity.

A thickness of the substrate layer may be appropriately selecteddepending on an application. Generally, a thickness of the conductiveresin film with substrate layer and the low-resistance layer combined is5 μm to 0.5 mm, preferably 10 μm to 200 μm. A volume resistance of theconductive resin film as a whole in a thickness direction is 0.01 to 5Ω, preferably 3 Ω or less.

There will be described a process for manufacturing a conductive resinfilm according to this aspect of the invention.

A substrate layer may be formed by a common process such as, but notlimited to, extrusion molding and roll forming.

A low-resistance layer may be formed by, without limitation, theprocess, in which a liquid composition of a fine carbon fiber and athermoplastic resin in a solvent is applied to a flat surface of asupport, dried or cured to form a low-resistance layer film on thesupport. Then, the support is placed such that the low-resistance layerside faces at least one side of a preformed substrate layer. Afterlaminating the substrate layer with the low-resistance layer by, forexample, thermocompression bonding, the support is peeled off. In aliquid composition, a fine carbon fiber may be dispersed while athermoplastic resin may be dissolved or partially or totally dispersed,preferably dissolved in a solvent.

The support may be selected from various known films; for example,polyesters, plycarbonates, triacetylcellulose, cellophane, polyamides,aromatic polyamides, polyimides, polyetherimides, polyphenylenesulfides,polysulfones, polyethersulfones and polypropylenes. For improvingreleasability between the low-resistance layer and the support, thesupport surface may be treated with a mold release such as a silicone.Among others, a polypropylene or polyester film is preferable because ofits proper strength, workability and cost.

A thickness of the support may be 5 to 500 μm, preferably 10 to 300 μm.If it is less than 5 μm, a substrate film has insufficient strength toprevent corrugation while if it is more than 500 μm, the film becomestoo sturdy to realize good handleability or workability.

A low-resistance layer according to this manufacturing process canexhibit good conductivity even when a rate of the fine carbon fiber islower because the fine carbon fiber is evenly dispersed in the resin. Ina conductive resin film of this aspect of the invention comprising thelow-resistance layer as an outermost layer, the fine carbon fiber isexposed in the surface, resulting in a significantly reduced contactresistance with contacting article.

This manufacturing process has an advantage that a substrate layer canbe formed by a common method with a good productivity such as extrusionmolding and roll forming, resulting in elimination of the problems offilm distortion, pinholes and residual solvents, easier formation of athick film and a higher productivity. In other words, this manufacturingprocess can solve the problems in both film properties and electricproperties.

This conductive resin laminated film is highly conductive and thus cansignificantly reduce a contact resistance with contacting article.Therefore, when being used as a member for, e.g., a storage device andan electric generator, it can dramatically reduce an internalresistance. Furthermore, since it is highly acid-resistant, it can beused particularly as a collector in an electric double layer capacitorcomprising an aqueous electrolytic solution.

An electric double layer capacitor which can comprise this conductiveresin film has, for example, a configuration as shown in FIG. 1. Whenlow-resistance layers are formed on both sides of a substrate layer, itscontact resistance with both polarizable electrode and externalconnection can be significantly reduced. Furthermore, when alow-resistance layer is formed on one side of a substrate layer, acontact resistance with one of the aboves can be significantly reduced.

<Second Aspect of the Invention: Monolayer Low-Resistance Film>

A second aspect of this invention relates to a monolayer low-resistanceconductive resin film. Specifically, it relates to a conductive resinfilm comprising a thermoplastic resin containing a fine carbon fiberhaving a fiber diameter of 0.001 to 0.5 μm and a fiber length of 0.1 to100 μm, wherein when a mixing volume ratio of the thermoplastic resin tothe fine carbon fiber is expressed by the equation:Thermoplastic resin/Fine carbon fiber=x/(100·x)and a volume resistance of the film is y in Ωcm, a coordinate point(x,y) in a x-y plane is within a range enclosed by a quadrangle withfour apices (50,0.01), (50,0.03), (90,0.1) and (90,0.5) including thelines and the apices.

Thus, a volume mixing ratio of the thermoplastic resin to the finecarbon fiber is thermoplastic resin/fine carbon fiber=50/50 to 90/10. Avolume resistance in a film with a volume mixing ratio of 50/50 is 0.01to 0.03 Ωcm, and a volume resistance in a film with a volume mixingratio of 90/10 is 0.1 to 0.5 Ωcm.

A conductive resin film according to this aspect of the invention is anovel film having a lower resistance, even if the amount of the finecarbon fiber contained is equal to that in a conventional film (forexample, Japanese Patent Laid-open Publication No. 1995-102112).

A thermoplastic resin can be, depending on an application, appropriatelyselected from the thermoplastic resins listed in “Resin as a filmcomponent”. Particularly preferred are polyolefin (PO) resins andpolyolefin elastomers; hydrogenated styrene elastomers such as SEBS; andfluororesins and fluoro-elastomers with good heat resistance and acidresistance.

The fine carbon fiber in the thermoplastic resin preferably has a fiberdiameter of 0.001 to 0.5 μm, preferably 0.005 to 0.3 μm and a fiberlength of 0.1 to 100 μm, preferably 0.5 to 30 μm in the light ofimproved conductivity, and may be combined with another carbonconductive material as a conductive agent. Examples of such anadditional carbon conductive material include artificial graphite,natural graphite, carbon black, exfoliated graphite, carbon fiber andshort carbon fiber.

Such a film may be formed by a variety of methods, but preferably by aprocess where a liquid composition of a fine carbon fiber and athermoplastic resin in a solvent is continuously applied to a flatsurface of a peelable support by an appropriate method such as diecoating, dried or cured, and a resulting coating film is peeled off fromthe support. In the liquid composition, the fine carbon fiber isdispersed while the thermoplastic resin may be dissolved or partially ortotally dispersed, preferably dissolved in a solvent.

In a film formed by this process, the fine carbon fiber is more evenlydispersed in the film than a film formed by dry blending and thenextrusion molding. Therefore, even a lower volume mixing ratio of thefine carbon fiber can adequately contribute to improving conductivity,resulting in a reduced internal resistance of the film. Furthermore,while a film formed by dry blending and then extrusion molding has alarger contact resistance with contacting article such as an electrodebecause of the presence of a resin skin layer in the film surface, afilm formed by the above inventive process can significantly reduce acontact resistance with a contacting article such as an electrodebecause a portion of the fine carbon fiber is exposed in the filmsurface.

A thickness of a conductive resin film according to the second aspect ofthe invention is preferably 10 to 200 μm. If it is less than 10 μm, afilm is so thin that it is easily broken or less handleable. If the filmthickness is more than 200 μm, a volume resistance in a thicknessdirection tend to be increased.

Since this film is highly conductive, it can dramatically reduce aninternal resistance, when used as a member for a storage device or anelectric generator and the like. Furthermore, since it is highlyacid-resistant, it can be used particularly as a collector in anelectric double layer capacitor comprising an aqueous electrolyticsolution, for example, as shown in FIG. 1.

<Third Aspect of the Invention: Collector for an Electric Double LayerCapacitor>

The third aspect of this invention relates to a collector for anelectric double layer capacitor, where a volume resistance of the filmin a thickness direction, i.e., in a direction perpendicular to the filmsurface is 0.01 to 5 Ωcm, preferably 0.01 to 3 Ωcm. The value less than0.01 Ωcm is impossible to achieve in practice, and that more than 5 Ωcmis inadequate for a collector in performance. A tensile breakingstrength as measured in accordance with JIS K7127 is 10 to 30 MPa,preferably 20 to 30M Pa. If it is less than 10 MPa, a collector is tooweak for practical use. If it is more than 30 MPa, a collector is toohard and the handling becomes more difficult.

Although both low resistance and high tensile strength are propertiesrequired in a collector, there have been no collectors meeting both ofthese requirements. Some of the conductive resin films according to thefirst and the second aspect of the invention described above can be usedas a collector in the third aspect of the invention.

A thermoplastic resin used in this embodiment may be selected from thethermoplastic resins described in “Resin as a film component”.Particularly preferred are fluororesins, fluoro-elastomers, polyolefinresins and polyolefin elastomers. Particularly preferred are PVDF, THV,VDF-HFP and TFE-P which contain vinylidene fluoride in the light ofmoldability, and are polyethylene, polypropylene and EPDM in the lightof heat resistance and moldability.

Examples of a conductive agent which can be suitably used in this aspectinclude carbon nanofiber, carbon nanotube and carbon nanohorn, metalcarbides and metal nitrides.

Carbon nanotube and carbon nanofiber preferably have a fiber diameter of0.001 to 0.5 μm, preferably 0.003 to 0.2 μm and a fiber length of 1 to100 μm, preferably 1 to 30 μm in the light of improving conductivity.The conductive agent may be combined with an additional carbonconductive agent. Examples of such an additional carbon conductive agentinclude artificial graphite, natural graphite, carbon black, exfoliatedgraphite and carbon fiber.

Preferred metal carbides are tungsten carbide, titanium carbide andchromium carbide exhibiting good conductivity and acid resistance.Preferred metal nitrides are titanium nitride and zirconium nitrideexhibiting good conductivity and acid resistance.

A ratio of the thermoplastic resin to the conductive agent is 50/50 to90/10 by volume, preferably 60/40 to 85/15 by volume. If a ratio of thethermoplastic resin to the conductive agent is less than 50/50 byvolume, a rate of the thermoplastic resin is too low to properly conductmolding. If it is more than 90/10 by volume, a rate of conductive agentis too low to achieve good conductivity.

A thickness of the conductive resin film including the thermoplasticresin and the conductive agent is desirably 0.01 mm to 0.5 mm. If thefilm thickness is less than 0.01 mm, the film is fragile and easilybroken, leading to poor handleability. If the thickness is more than 0.5mm, a collector is so thick that an internal resistance in an electricdouble layer capacitor is increased and the size an electric doublelayer capacitor is increased.

The conductive resin film for a collector may be manufactured by, butnot limited to, a common extrusion molding or roll forming process. Forexample, a thermoplastic resin and a conductive agent are premixed by anappropriate apparatus such as a twin screw extruder, and the mixture maybe processed by extrusion molding or roll forming to form a conductiveresin film. As described in “the Second Aspect”, a film may be formed byapplying the mixture to a flat surface of a peelable support, drying orcuring, and then peeling a film from the support.

When using such a conductive resin film as a monolayer, a collectorsatisfying both volume resistance of 0.01 to 5 Ωcm and tensile breakingstrength of 10 to 30 MPa can be provided by properly selecting a resinand a conductive agent as well as, for example, a mix proportionthereof.

In order to further reduce a contact resistance with an electrode, it ispreferable to form a low-resistance layer on at least one side of theconductive resin film.

A low-resistance layer may be formed by forming a resin layer containinga conductive agent on a conductive resin film surface or burying aconductive agent in a conductive resin film surface. Examples of aconductive agent may include carbon conductive agents, metal carbideconductive agents and metal nitride conductive agents as described in“Conductive agent”. Specifically, a dispersion of a conductive agentalone in a solvent or appropriately in combination with a thermoplasticresin, depending on the type of the conductive agent used (preferably,the resin is dissolved) is applied to a peelable support, dried or curedto form a conductive agent layer. After transferring it to a conductivesubstrate layer, (a conductive resin film separately formed), thesupport is peeled off and a low-resistance layer is attached to form thelow-resistance layer. The support may be a polyester film and the like.

An example of such a collector having a low-resistance layer in itssurface is a conductive resin film comprising a low-resistance layer asdescribed in the first aspect, that is, a layer having a volumeresistance of 0.1 to 1.0 Ωcm on the outermost layer in the substratelayer. Depending on the type of a conductive agent, for example aparticulate agent such as tungsten carbide may be buried in a surface (athermoplastic resin may be added as a binder).

A collector comprising a conductive resin film having a low-resistancelayer in its surface has an advantage that since a conductive agent isdispersed in the surface with a higher density, a volume resistance ofthe overall film in a thickness direction can be reduced. Thus, since arelatively lower amount of a conductive material contained in asubstrate layer may give sufficient conductivity to the collector, bothrequirements of a lower resistance and a higher tensile breakingstrength can be achieved.

EXAMPLES

This invention will be described with reference to, but not limited to,Examples.

<Measuring Methods of a Volume Resistance in a Thickness Direction>

A volume resistance of a layer or film in this example in a thicknessdirection (a direction perpendicular to a film surface) was evaluated asfollows.

1. Measuring Apparatus

Resistance meter: Type YMR-3 (Yamasaki-seiki Co., Ltd.)

Loading device: Type YSR-8 (Yamasaki-seiki Co., Ltd.)

Electrodes: Two brass plates (Area: 6.45 cm², mirror finished,gold-plated surface).

2. Measurement Conditions

Method: Four terminal method

Applied current: 10 mA (alternating current, 287 Hz)

Open-terminal voltage: 20 mV peak or less

Load (pressure): 1.8 MPa (18.6 kgf/cm²).

3. Measuring Method

Using the measuring apparatus as shown in FIG. 2, a measured sample 12was sandwiched by brass electrodes 11, and while applying a given load(pressure), a voltage at a given current was determined by afour-terminal method.

4. Method for Calculating a Volume Resistance

From the resistance R (Ω) as determined by the above method, anelectrode area (6.45 cm²) and a sample thickness t (cm), a volumeresistance in a thickness direction can be calculated by the equation:Volume resistance in a thickness direction (Ωcm)=R×(6.45 cm² /t).<<Examples of the First Aspect >><Formation of a Substrate Layer>

A thermoplastic resin and a conductive agent were mixed by a twin screwextruder (an extruder temperature: 230° C.) in a ratio described inTable 1.

The resulting mixture was extruded from a nozzle by a single screwextruder (an extruder temperature: 230° C.) to form a conductivesubstrate film.

All of the resulting substrate films have a thickness of 100 μm, andvolume resistances in a film thickness direction are shown in Table 1.

The thermoplastic resins and the conductive agents in Table 1 are asfollows.

1. Polyolefin Elastomer

“T310E”, Idemitsu Kosan Co., Ltd., specific gravity: 0.88

2. Styrene elastomer

“Tuftec H1041”, Asahi Kasei Corporation, specific gravity: 0.91

3. Fluoro-Elastomer

“THV220G”, Sumitomo 3M Ltd., specific gravity: 2

4. Carbon Black

Ketjen Black, Lion Corporation, specific gravity: 1.5

5. Artificial Graphite Powder

“UFG-30”, Showa Denko K.K., specific gravity: 2.2

6. Titanium Carbide

“Titanium carbide”, Allied Material Corp. specific gravity: 4.9

<Formation of Low-Resistance Layer A>

SEBS (Tuftec H1041, Asahi Kasei Corporation, specific gravity: 0.91) anda fine carbon fiber (“Vapor deposition carbon fiber VGCF”, Showa DenkoK.K., specific gravity: 2) in a ratio of 60/40 were mixed in THF(tetrahydrofuran) such that a solid concentration was 8 wt %, to preparea dispersion.

The fine carbon fiber used had a fiber diameter of 150 nm, a fiberlength of 10 to 20 μm, a bulk specific gravity of 0.035 g/cc and a truespecific gravity of 2.0 g/cc.

The dispersion was applied on a support (polypropylene film:thickness=50 μm) using a bar coater (Matsuo Sangyo Co. Ltd., No. 70) anddried at 80° C. to form a laminate of support and low-resistance layer.

Low-resistance layer A was removed from the resulting laminate ofsupport-low-resistance layer composite. Low-resistance layer A wasmeasured for its thickness and volume resistance, giving a thickness of20 μm and a volume resistance in a thickness direction of 0.94 Ωcm.

<Formation of Low-Resistance Layer B>

A fluoro-elastomer (THV220G, Sumitomo 3M Ltd., specific gravity: 2) anda fine carbon fiber (“Vapor deposition carbon fiber VGCF”, Showa DenkoK.K., specific gravity: 2) in a volume ratio of 60/40 were mixed in MIBK(methyl isobutyl ketone) such that a solid concentration was 8 wt %, toprepare a dispersion.

The fine carbon fiber used had a fiber diameter of 150 nm, a fiberlength of 10 to 20 μm, a bulk specific gravity of 0.035 g/cc and a truespecific gravity of 2.0 g/cc.

The dispersion was applied on a support (polypropylene film:thickness=50 μm) using a bar coater (Matsuo Sangyo Co. Ltd., No. 70) anddried at 80° C. to form a laminate of support-low-resistance layercomposite.

Low-resistance layer B was removed from the resulting laminate ofsupport-low-resistance layer composite. Low-resistance layer B wasmeasured for its thickness and volume resistance, giving a thickness of20 μm and a volume resistance in a thickness direction of 0.73 Ωcm.

Examples 1 to 6

<Formation of a Conductive Resin Laminate Film>

The substrate film prepared as described above and low-resistance layerA and/or B in a combination described in Table 2 were placed in thesequence of (low-resistance layer)/(substrate layer)/(low-resistancelayer), and laminated by hot press to form a conductive resin laminatefilm.

The hot-press conditions were a heating temperature of 140° C. and apressure of 4.9×10⁶ Pa (50 kgf/cm²).

The conductive resin laminate films thus obtained had a thickness of 130μm and a volume resistance in a thickness direction shown in Table 2.TABLE 1 Resin composition Conductive agent Volume (volume %) (volume %)resistance Substrate 1 Polyolefin elastomer Carbon black (12%)  8.2 Ωcm(88%) Substrate 2 Styrene elastomer (88%) Carbon black (12%) 29.8 ΩcmSubstrate 3 Polyolefin elastomer Artificial graphite 20.2 Ωcm (40%)powder (60%) Substrate 4 Styrene elastomer (40%) Artificial graphite16.5 Ωcm powder (60%) Substrate 5 Polyolefin elastomer Titanium carbide50.3 Ωcm (65%) (35%) Substrate 6 Fluro-elastomer (70%) Titanium carbide41.1 Ωcm (30%)

TABLE 2 Volume Substrate layer Low-resistance layer resistance Example 1Substrate 1 Low-resistance layer A 1.66 Ωcm Example 2 Substrate 2Low-resistance layer A 2.41 Ωcm Example 3 Substrate 3 Low-resistancelayer A 1.87 Ωcm Example 4 Substrate 4 Low-resistance layer A 1.76 ΩcmExample 5 Substrate 5 Low-resistance layer A 2.01 Ωcm Example 6Substrate 6 Low-resistance layer B 1.89 Ωcm

The results in Table 2 shows that a conductive resin laminate filmcomprising a low-resistance layer formed according to the process ofthis invention has a considerably lower volume resistance in a filmthickness direction, i.e., better conductivity, than that in theconductive film without a low-resistance layer in Table 1.

FIGS. 3A and 3B are SEM images of a cross-section and a surface of aconductive resin whose surface has a low-resistance layer comprising afine carbon fiber as a conductive agent, respectively. These mayindicate that using a particular fine carbon fiber, a conductive agentis exposed in a surface and thus an opportunity of direct contactbetween a contacting article and the conductive agent is increased,resulting in a lower contact resistance.

Example of the Second Aspect

A fluoro-elastomer (THV220G, Sumitomo 3M Ltd., specific gravity: 2) anda fine carbon fiber (“Vapor deposition carbon fiber VGCF”, Showa DenkoK.K., specific gravity: 2) in a volume ratio of 50/50, 60/40, 70/30,80/20 or 90/10 were mixed in MIBK (methyl isobutyl ketone) such that asolid concentration was 20 wt %, to prepare five dispersions.

The fine carbon fiber used had a fiber diameter of 150 nm, a fiberlength of 10 to 20 μm, a bulk specific gravity of 0.035 g/cc and a truespecific gravity of 2.0 g/cc.

Each of these five dispersions was applied on a polyester film with athickness of 200 μm by die coating, dried in an oven furnace until aresidual solvent concentration became 0.1% by weight or less, and thenremoving the polyester film, to give five conductive films. All of thesefive conductive films had a thickness of 100 μm.

Referential Example

As a reference example, a fluoro-elastomer (THV220G, Sumitomo 3M Ltd.,specific gravity: 2) and a fine carbon fiber (“Vapor deposition carbonfiber VGCF”, Showa Denko K.K., specific gravity: 2) in a volume ratio of50/50, 60/40, 70/30, 80/20 or 90/10 were mixed in a twin screw extruder(a mixing temperature: 250° C.) and extruded from a nozzle in an attemptto form a conductive film. However, in the case of a volume ratio offluororesin/fine carbon fiber of 50/50 or 60/40, the amount of the finecarbon fiber was too high to be mixed in the resin, and thus only threeconductive films with a volume ratio of 70/30, 80/20 and 90/10 wereprepared. All of these three conductive films had a thickness of 100 μm.

In these example and referential example, a resulting conductive filmwas measured for its volume resistance in accordance with JIS K 7194 bythe following measuring method, which determines a volume resistivity ofthe whole film.

1. Measuring Apparatus

Loresta HP (Mitsubishi Chemical Corporation)

2. Measuring Method

Four-terminal four-probe method (ASP type probe)

3. Applied Current During Measurement

100 mA

Table 3 shows volume resistance values measured by the above method.TABLE 3 Volume resistance of a conducive film Volume rate Volume rate ofa Referential of a resin fine carbon fiber Example Example 50% 50% 0.02Ω A film could not be formed. 60% 40% 0.05 Ω A film could not be formed.70% 30% 0.08 Ω 0.24 Ω 80% 20% 0.11 Ω 1.20 Ω 90% 10% 0.27 Ω   50 Ω

As shown in Table 3, a conductive film comprising a fine carbon fiberformed by the process of this invention has a volume resistance within arange acceptable in this invention and has a considerably lower volumeresistance, i.e., better conductivity, than that in a conductive filmwith the same composition formed by extrusion.

Examples of the Third Aspect Example C-1

In a twin extruder (an extruder temperature=250° C.) were mixed 23 partsby weight (volume rate: 70%) of a fluororesin (THV220G, Sumitomo 3MLtd., specific gravity: 2) and 77 parts by weight (volume rate: 30%) ofa conductive filler (Tungsten carbide WC20, Allied Material Corp.specific gravity: 15.5).

The resulting mixture was extruded from a nozzle using a single screwextruder (an extruder temperature=250° C.), to form a conductive resinfilm. The resulting conductive resin film (Sample 1) had a thickness of0.3 mm.

Example C-2

In a twin extruder (an extruder temperature=250° C.) were mixed 70 partsby weight (volume rate: 70%) of a fluororesin (THV220G, Sumitomo 3MLtd., specific gravity: 2) and 30 parts by weight (volume rate: 30%) ofa carbon nanotube (Vapor deposition carbon fiber VGCF, Showa Denko K.K.,specific gravity: 2). The carbon nanotube had a diameter of 0.15 μm, alength of 1 to 20 μm and a bulk specific gravity of 0.04 g/cm³.

The resulting mixture was extruded from a nozzle using a single screwextruder (an extruder temperature=250° C.), to form a conductive resinfilm. The resulting conductive resin film (Sample 2) had a thickness of0.3 mm.

Comparative Example C-1

In a twin extruder (an extruder temperature=250° C.) were mixed 75 partsby weight (volume rate: 70%) of a fluororesin (THV220G, Sumitomo 3MLtd., specific gravity: 2) and 25 parts by weight (volume rate: 30%) ofa short carbon fiber (HTA-0040, TOHO TENAX Co., Ltd., specific gravity:1.77). The short carbon fiber had a diameter of 4 to 7 μm, a length of40 to 1,000 μM and a bulk specific gravity of 0.07 g/cm³.

The resulting mixture was extruded from a nozzle using a twin screwextruder (an extruder temperature=250° C.), to form a conductive resinfilm. The resulting conductive resin film (Sample 3) had a thickness of0.3 mm.

Comparative Example C-2

In a twin extruder (an extruder temperature=250° C.) were mixed 63 partsby weight (volume rate: 60%) of a fluororesin (THV220G, Sumitomo 3MLtd., specific gravity: 2) and 37 parts by weight (volume rate: 40%) ofa short carbon fiber (HTA-0040, TOHO TENAX Co., Ltd., specific gravity:1.77). The short carbon fiber was as used in Comparative Example 1. Theresulting mixture was extruded from a nozzle using a twin screw extruder(an extruder temperature=250° C.), to form a conductive resin film. Theresulting conductive resin film (Sample 4) had a thickness of 0.3 mm.

A volume resistance in a thickness direction for the above sample filmswas determined as described in “Measuring methods of a volume resistancein a thickness direction”.

A tensile breaking strength for the sample films was determined inaccordance with IS K7127 as described below.

1. Tension Tester

Universal testing machine

2. Test Temperature

23° C.

3. Shape of a Test Piece

Type 2 test piece

4. Testing Rate

50.0 mm/min

Table 4 shows the results of a volume resistance and a tensile breakingstrength. TABLE 4 Resin Conductive agent Volume resistance Tensilebreaking Example Resin Name Vol % Conductive agent Vol % (Ωcm) strength(MPa) Example C-1 Sample 1 THV 220 70% Tungsten carbide 30% 1.3 19.6Example C-2 Sample 2 THV 220 70% Carbon nanotube 30% 0.52 25.5Comparative Example C-1 THV 220 70% Short carbon fiber 30% 55 15.5Sample 3 Comparative Example C-2 THV 220 60% Short carbon fiber 40% 4.85.0 Sample 4

As shown in Table 4, Sample 1 comprising tungsten carbide and Sample 2comprising carbon nanotube having a volume resistance of 0.01 to 5 Ωcmexhibited better conductivity than Sample 3 comprising short carbonfiber in a fluororesin. Sample 4 comprising more short carbon fiber in afluororesin that Sample 3 has a lower volume resistance, but a lowertensile breaking strength. However, the conductive resin films of Sample1 comprising tungsten carbide and Sample 2 comprising carbon nanotubewhich have a volume resistance within a range acceptable in thisinvention have a higher and sufficient tensile breaking strength of 10to 30 MPa.

Example C-3

In this example, low-resistance layers were formed as surface layers.

Formation of a Low-Resistance Layer

A fluoro-elastomer (THV220G, Sumitomo 3M Ltd., specific gravity: 2) anda fine carbon fiber (“Vapor deposition carbon fiber VGCF”, Showa DenkoK.K., specific gravity: 2) in a volume ratio of 55/45 were mixed in MIBK(methyl isobutyl ketone) such that a solid concentration was 8 wt %, toprepare a dispersion.

The fine carbon fiber used had a fiber diameter of 150 nm, a fiberlength of 10 to 20 μm, a bulk specific gravity of 0.035 g/cc and a truespecific gravity of 2.0 g/cc.

The dispersion was applied on a support (polypropylene film:thickness=50 μm) using a bar coater (Matsuo Sangyo Go. Ltd., No. 70) anddried at 80° C. to form a laminate of support-low-resistance layercomposite.

A low-resistance layer was removed from the resulting laminate ofsupport-low-resistance layer composite. Low-resistance layer B wasmeasured for its thickness and volume resistance, giving a thickness of20 μm and a volume resistance in a thickness direction of 0.65 Ωcm.

Formation of a Conductive Resin Film

The conductive resin film (Sample 3) obtained in Comparative Example C-1was used as a substrate layer and the above low-resistance layer wereplaced in the sequence of low-resistance layer/substrate layer (Sample3)/low-resistance layer, and laminated by hot press to form a conductiveresin film comprising the low-resistance layer.

The hot-press conditions were a heating temperature of 140° C. and apressure of 4.9×10⁶ Pa (50 kgf/cm²).

The conductive resin film thus obtained had a thickness of 330 μm, andits volume resistance in a thickness direction and tensile breakingstrength are shown in Table 5. TABLE 5 Low- Volume Substrate resistanceresistance Tensile breaking Example layer layer (Ωcm) strength (MPa)Example C-3 Sample 3 Both sides 4.1 15.4

As shown in Table 5, the formed film comprising a low-resistance layerin both sides of Sample 3 has a tensile strength substantiallycomparable to Sample 3 and a significantly lower volume resistance in afilm thickness direction than Sample 3. Thus, it was a formed filmmeeting the requirements for both lower resistance and higher tensilebreaking strength.

INDUSTRIAL APPLICABILITY

A conductive resin film according to this invention has a lower volumeresistance particularly in a film thickness direction and improvedcorrosion resistance, and can be manufactured in a relatively lowercost. It can be, therefore, used in, for example, a collector for anelectric double layer capacitor.

1. A conductive resin film comprising a conductive substrate layer and alow-resistance layer with a volume resistance of 0.1 to 1.0 Ωcm in athickness direction as at least one of its outermost layer.
 2. Theconductive resin film as claimed in claim 1, wherein a volume resistanceof the low-resistance layer in a thickness direction is ⅕ or less of avolume resistance of the substrate layer in a thickness direction. 3.The conductive resin film as claimed in claim 1, wherein thelow-resistance layer is a layer in which the thermoplastic resincomprises a fine carbon fiber with a fiber diameter of 0.003 to 0.5 μmand a fiber length of 0.1 to 100 μm as a conductive agent.
 4. Theconductive resin film as claimed in claim 1, wherein a thickness of thelow-resistance layer is 1 to 50 μm.
 5. The conductive resin film asclaimed in claim 1, wherein the substrate layer comprises a conductiveagent selected from the group consisting of graphite powder, exfoliatedgraphite, carbon black, carbon fiber, carbon nanofiber, carbon nanotube,a metal carbide, a metal nitride, a metal oxide, metal fiber and metalpowder.
 6. A process for manufacturing a conductive resin film asclaimed in claim 1, comprising the steps of applying a liquidcomposition of a fine carbon fiber and a thermoplastic resin in asolvent to a flat surface of a support, followed by drying or curing toform a coating film; placing the coating film over at least one side ofa conductive substrate layer; and performing a lamination.
 7. Aconductive resin film as claimed in any of claim 1 used as a collectorfor an electric double layer capacitor.
 8. A collector for an electricdouble layer capacitor comprising the conductive resin film as claimedin claim
 7. 9. A conductive resin film comprising a thermoplastic resincontaining a fine carbon fiber having a fiber diameter of 0.001 to 0.5μm and a fiber length of 0.1 to 100 μm, wherein when a mixing volumeratio of the thermoplastic resin to the fine carbon fiber is expressedby the equation:Thermoplastic resin/Fine carbon fiber=x/(100−x) and a volume resistanceof the film is y in Ωcm, a coordinate point (x,y) in a x-y plane iswithin a range enclosed by a quadrangle with four apices (50,0.01),(50,0.03), (90,0.1) and (90,0.5) including the lines and the apices. 10.The conductive resin film as claimed in claim 9, wherein a thickness ofthe conductive resin film is 10 to 200 μm.
 11. A process formanufacturing a conductive resin film as claimed in claim 9, comprisingthe steps of applying a liquid composition of a fine carbon fiber havinga fiber diameter of 0.001 to 0.5 μm and a fiber length of 0.1 to 100 μmand a thermoplastic resin in a solvent to a flat surface of a support,followed by drying or curing to form a coating film; and then peelingthe coating film from the support.
 12. A conductive resin filmmanufactured by the process as claimed in claim
 11. 13. The conductiveresin film as claimed in claim 9 used as a collector for an electricdouble layer capacitor.
 14. A collector for an electric double layercapacitor comprising the conductive resin film as claimed in claim 13.15. A collector for an electric double layer capacitor consisting of aconductive resin film comprising a thermoplastic resin containing aconductive agent, wherein the film has a volume resistance in athickness direction of 0.01 to 5 Ωcm and a tensile breaking strength of10 to 30 MPa as measured in accordance with JIS K7127.
 16. The collectorfor an electric double layer capacitor as claimed in claim 15, whereinthe thermoplastic resin is selected from the group consisting offluororesins, fluoro-rubbers, polyolefins and polyolefin elastomers. 17.The collector for an electric double layer capacitor as claimed in claim15, wherein the conductive agent is selected from the group consistingof carbon nanotube, carbon nanofiber, a metal carbide and a metalnitride.
 18. The collector for an electric double layer capacitor asclaimed in claim 15, wherein a volume ratio of the thermoplastic resinto the conductive agent is 50/50 to 90/10.
 19. The collector for anelectric double layer capacitor as claimed in claim 15, wherein athickness of the conductive resin film is 0.01 mm to 0.5 mm.
 20. Thecollector for an electric double layer capacitor as claimed in claim 15,wherein at least one side of the conductive resin film comprises alow-resistance layer.
 21. A process for manufacturing a collector for anelectric double layer capacitor as claimed in claim 15, comprising thesteps of forming a conductive layer on a peelable support, placing theconductive layer with the support over at least one side of theconductive substrate layer to transfer the conductive layer, and peelingthe support to form a low-resistance layer on the surface of theconductive resin film.
 22. A collector for an electric double layercapacitor manufactured by the process as claimed in claim
 21. 23. Thecollector for an electric double layer capacitor as claimed in claim 15,wherein the electric double layer capacitor comprises an aqueouselectrolytic solution.